What is the Difference between Hot Runner and Cold Runner Injection Molding?

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Hot Runner Molds

Two plates make up a hot runner mold. These plates are heated through the use of a manifold system. Both externally and internally heated hot runners are available for use. For materials that are particularly sensitive to heat, externally heated molds are preferred. When enhanced flow control is desired, internally heated molds are the better option. The methods available to heat runners include heating rods, coils, and heating pipes. A hot runner system keeps material in a molten state during the duration of the runner process until it flows into the mold cavity.

Cold Runner Molds

In a cold runner system, the runners and the molds are maintained at the same temperature. Within this system, two or three plates are contained within the mold. The two plate system is easier to use, but requires an injection system to remove the part from the mold. Within a three-plate system, the runner functions on a separate plate. Therefore, it can be ejected separately from the runner. A three-plate cold runner mold allows for flexibility in design. To ensure the mold is not under filled in that the material fills the part properly, the runner dimension must be larger than the part within this system.

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